Is Your Child's Food Allergy Testing Right?

Your child has tested positive for a food allergy, but can the allergy testing results be trusted? The odds say probably not - it takes more than a simple blood test to determine whether your child has a bona fide food allergy.

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Parents of kids with a food allergy bend over backward to make sure their child doesn't eat anything that could trigger a potentially serious reaction. But what if the initial allergy testing, precautions, special diets, and anxiety over food turn out to be needless? It happens - food allergies in kids are often misdiagnosed.

No doubt, millions of American children have true food allergies. The U.S. Centers for Disease Control and Prevention estimates that 40 percent of kids under age 18 have a food allergy. Peanut allergy is perhaps the most well known, but other common culprits in kids are:

Milk

Eggs

Fish

Wheat

Soy

A food allergy is an immune system problem. Your body fights a protein in a certain food by forming antibodies (called immunoglobulin E or IgE) to fight what it perceives as a threat, causing allergic symptoms. Food intolerances can be confused with allergy, but are digestion problems. For instance, people with lactose intolerance can't digest milk products correctly, but they don't have a milk allergy.

Allergy Testing: What It Takes to Get It Right

Food allergy misdiagnosis is becoming a concern for doctors, says Daniel Searing, MD, a pediatrician in the department of pediatrics, division of allergy and immunology, at National Jewish Health in Denver. A big part of the problem is that too much emphasis is being placed on the results of allergy blood tests, Dr. Searing says. These tests look for the presence of IgE to a questionable food. In many cases, kids are put on a restricted diet solely because of a positive blood test.

But Searing says blood tests aren't a definitive diagnostic tool; rather they can help doctors determine the likelihood of an allergic reaction. "A large number of patients can still tolerate foods that they make allergic antibodies to," he says. "Patients who have elevated allergic antibodies to foods need to have [the antibodies] evaluated by an allergist to help determine if the patient needs to avoid the food or could potentially continue to eat it."

"Food allergies are complicated and can be daunting for parents," Searing says. However, a comprehensive food allergy evaluation can determine if your child really has a food allergy. Blood tests are one important component of an evaluation. Here's what else is involved:

Detailed history of reactions. There are many symptoms of an allergic reaction, but typical ones are sneezing, wheezing, hives, and abdominal pain. A serious reaction can be fatal. Your doctors will ask what your child has been eating. What were her reactions and how serious were the problems? How quickly did the symptoms occur? (In an allergic reaction, symptoms usually appear shortly after the food is eaten.) Keeping a record of your child's history that includes the food eaten, the reaction, and other details, can give the doctor solid information.

Skin prick tests. These are especially helpful in ruling out allergies. After a negative test, there's a 95 percent chance your child will not develop an allergic reaction after eating the tested food, Searing says. In this test, a small amount of each suspected allergen is placed on your child's back. The skin is pricked. If a bump or redness appears, that's a positive test. Still, that doesn't mean if your child ate the food that she would have allergic reaction. Half of all positive skin tests are false-positives, according to Searing.

Oral food challenges. Sometimes even after blood and skin tests, questions about allergies remain. The oral food challenge test is considered the gold standard of allergy tests because it can provide a definitive diagnosis. In a highly medically supervised setting, your child eats food she has been avoiding because of allergy fears. At first, your child is given a small amount of a suspect food and allergists watch for reactions. If none occurs, your child receives increasingly larger servings. If your child has no symptoms after eating a full serving of the food, it can be safely included in the diet.

Searing says the process is time-consuming, but can be very rewarding. Sometimes long-avoided foods can be reintroduced, making life a lot easier for kids and their families. A recent chart review of 115 kids given a full allergy evaluation at National Jewish Health and a Denver-area clinic demonstrates the benefit of food challenges. The children were originally diagnosed with food allergies based on blood tests and were not eating suspect foods. One hundred forty two food challenges were completed and a majority - 77 percent - tested negative, meaning many of the kids weren't allergic to foods they had been avoiding.

Another point to note is that not all food allergies remain a permanent issue. While a peanut allergy often lasts a lifetime, most kids with milk and egg allergies outgrow them by the time they start kindergarten. So it's important for parents to have their kids see their allergist every year for a new analysis, Searing says.

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